Module
ActionDispatch::Routing::UrlFor

In config/routes.rb you define URL-to-controller mappings, but the
reverse is also possible: an URL can be generated from one of your routing
definitions. URL generation functionality is centralized in this module.

Tip: If you need to generate URLs from your models or some other
place, then ActionController::UrlFor is
what you’re looking for. Read on for an introduction.

URL generation from parameters

As you may know, some functions, such as ActionController::Base#url_for and
ActionView::Helpers::UrlHelper#link_to,
can generate URLs given a set of parameters. For example, you’ve probably
had the chance to write code like this in one of your views:

link_to, and all other functions that require URL generation functionality,
actually use ActionController::UrlFor
under the hood. And in particular, they use the
ActionController::UrlFor#url_for method. One can generate the same path as
the above example by using the following code:

Notice the :only_path => true part. This is because UrlFor has no information about the website hostname
that your Rails app is serving. So if you
want to include the hostname as well, then you must also pass the
:host argument:

By default, all controllers and views have access to a special version of
url_for, that already knows what
the current hostname is. So if you use url_for in your controllers or your
views, then you don’t need to explicitly pass the :host
argument.

For convenience reasons, mailers provide a shortcut for
ActionController::UrlFor#url_for. So within mailers, you only have to type
‘url_for’ instead of
‘ActionController::UrlFor#url_for’ in full. However, mailers don’t
have hostname information, and what’s why you’ll still have to specify
the :host argument when generating URLs in mailers.

URL generation for named routes

UrlFor also allows one to access methods that
have been auto-generated from named routes. For example, suppose that you
have a ‘users’ resource in your config/routes.rb:

resources :users

This generates, among other things, the method users_path. By
default, this method is accessible from your controllers, views and
mailers. If you need to access this auto-generated method from other places
(such as a model), then you can do that by including ActionController::UrlFor in
your class: